There is a correlation between interstitial pH of cardiac tissue during coronary artery bypass surgery and the resultant postoperative viability of the heart, and consequently the patient. Randolph, J. D. et al., J. Vasc. Sur., 3, No. 2, 216-224 (February 1986); and Khuri et al., J. Thoracic and Cardiovascular Surgery, 86, No. 5, 667-78 (1983).
Khuri et al. concluded that the magnitude of rise in intramyocardial pH and myocardial temperature during the period of aortic cross-clamping is a good indicator of the adequacy of myocardial preservation; and that during periods of aortic cross-clamping exceeding 40 minutes, myocardial temperature is a poor indicator of adequacy of preservation since progressive tissue acidosis may progress despite low myocardial temperatures. Khuri et al. further concluded that techniques and solutions that can effectively reduce the progression of tissue acidosis will likely enhance the clinician's ability to protect the ischemic myocardium during cardioplegic arrest. Khuri 86, at 667; see also Khuri, S. F., Cardiac Surgery: State of the Art Reviews, “Myocardial Preservation During Coronary Artery Bypass Surgery,” 1, No. 1, 59-75 (October 1986).
Acidosis is a condition associated with the deprivation of oxygen in the tissue being monitored. Lack of oxygen causes a buildup of hydrogen ions, which can be measured by pH sensors. Preferred pH sensors are described in contemporaneously filed U.S. Application No. 60/434,815, entitled, “Miniature Electrode for Detecting Interstitial Tissue pH”, which is incorporated herein by reference. Severe acidosis is associated with a poor prognosis following cardiac bypass surgery.